Quad II test run.

[Radio Wrangler]

Yes, I think I listed three turrets to be linked together. put the earth clips of both scope probes onto them as well. That'll fix the problem and make the tests work.

David

[julie_m]

The clue should be in the name. A word that ends in meter means an instrument for measuring something. A word that ends in scope means an instrument for viewing something. They're not necessarily the same thing.

A voltmeter gives you a nice accurate reading, but it takes some time to gather that reading in the first place and it can't change instantaneously (either because the needle takes some finite time to move; or because converting an analogue value to digital takes some finite time, and more if it's precision you want).

An oscilloscope gives you a quick and dirty guess -- or rather, it gives you lots of quick and dirty guesses in rapid succession, and draws a graph with time on the X-axis. Where something is changing too fast for a meter to respond to, that's important.

Given a DC-coupled amplifier with a 37V power rail, if you try powering it up with no speaker and no input signal, what would you probe the output with? If you use a meter, you might see 19.1V, spend too much time arguing over whether that was too high for the expected 18V5 and miss the real fault. If you use an oscilloscope, the first thing you might see is it's somewhere between 15V and 20V, which is certainly not egregiously out-of-range; but then if you see the trace suddenly going wild, you'll know for sure what is going on.

I'm personally convinced that much of the "anti-oscilloscope bias" is mostly for the sake of convincing the hater themself that they do not really need to own such an expensive, finicky instrument -- or that one within their budget can't possibly be any good. But times have changed; and you can obtain a 20MHz analogue instrument for next to nothing, or a simple battery hand-held digital one for not much more. And they are also easier to use thanks to automatic range and timebase selection and triggering. Of course such an oscilloscope will have limitations compared to a top-of-the-range unaffordable one; but it would have to be really lousy not to beat the daylights out of not having one!

[Radio Wrangler]

Originally Posted by julie_m

a top-of-the-range unaffordable one;

Even that's changed, Julie. Serious scopes are available cheaply. Sitting not too far from me is a Tektronix 465B in full working order..... £70 didn't break the bank. Tektronix is the rolls-royce of scopes. 100MHz, 4 channels, 5mV/div sensitivity, dual timebases and all sorts of tricks.

But is it suitable for a beginner? is a common question. Id doesn't appear so, but if someone gets shown how to set it up for basic measurements, it'll do fine. Then as they get more experienced and more adventurous they can try out some of the added bells and whistles but they still know how to drive the basic scope underlying it all.

If they'd gone for a very basic educational scope, they'd have soon hit its limits and had to change to a more comprehensive model and had to start learning all of that machine from scratch.

But the belief lives on that some instruments are too much. Too complicated, too difficult. I suppose it keeps the prices down for those of us not scared by them.

If I have seen further than others, it's because I've been standing on a pile of old test equipment... I must get round to fixing it one day

David

[Ted Kendall]

I got into using 'scopes almost from the off - my first was a Panax with EF50s and a wonky timebase, but still useful in a way meter could never be. Why grope at a problem through a blanket when you can easily remove it and take a look?

[sparkymike]

Hi David, some years ago I was involved with a special truck mounted container for for Racal ,for radio com. use by the UK army. This was built on the Faraday principle, and all sorts of weird ideas were incorporated in the contruction.
Mike.

[Radio Wrangler]

They might have called it Faraday, but I think they would have been really disappointed if it had been.

Electric fields are easy to screen, it's the magnetic fields which are real b*ggers. So you'll find an attempt to make an all metal seamless enclosure, doors close with knife-edge flanges plugging into spring-finger stuffed channels.

The idea is that a fully enclosing metal surface repels magnetic components by means of eddy currents.

To protect radio comms gear you need a real screen one that stops everything. A Faraday screen is not good enough, a faraday screen is one specially designed to let stuff through. Think of colendar when you want a pressure cooker.

David

[sparkymike]

Right David, did that test. With the probe on either U W X or Y no change from the a/c wave from L/T supply and other trace is this weird looking trace with like a sharp peak in it. These two traces stay the same all the time. I tried to take a pic, but sun is shining in at the moment. I may get better luck after tea.
Mike.

[Radio Wrangler]

It's beginning to look that way. I wasn't able to follow post 147, though.

David

[sparkymike]

As a matter of interest,and now I am more confident using the scope, I have repeated GJ's test in post 50. Results are same as in that post with the exception of W is out of phase and U is in phase. Could this be that U and W have been tagged wrong and have been soldered in wrong turrets ?
Mike.

[Radio Wrangler]

First photo shows two signals in antiphase. the second shows two in phase, but as I don't know which is what, I'm afraid I'm lost.

I'm assuming one of those traces is the same on both pictures and is a probe on Q

Then one picture shows U and the other one W

Now, I think (and it hasn't been checked by anybody yet) that U should be in antiphase and W should be in-phase.

Don't post pictures of scope displays without saying exactly what's on them. Each does need to be accompanied by full descriptive text to make sense.

David

[sparkymike]

Hi David, it is marked on the bottom of the photos, which is which.
Mike.

[Boulevardier]

One photo is labelled "W", but shows two traces; the other photo is labelled "U", but similarly shows two traces. We are not told what the second trace on each photo is, and if we were told we would need to know which was which on each photo.

For some reason, I am finding this the most confusing thread I've ever read on this forum!

Mike

[Radio Wrangler]

Hadn't spotted that So W is in antiphase with Q. U is in phase with Q
Now My reckoning was that it should be the other way round.

Both signals are the same amplitude, which is good, so it looks like the leadout wires from the transformer windings to the U and W turret tags are reversed. If you can swap them within the transformer then the signals on the turrets should become right. Then if you double check the turrets are wires to the right valves, then the amplifier might just work.

David

[PJL]

Originally Posted by sparkymike

Hi PJL,
results of your test.
Channel 1 T turret. 8 volts A/C
Channel 2
W out of phase. 8 volts
U in phase 8 volts
X out of phase 74 volts
Z in phase 74 volts
Mike.

This confirms the findings in post #93. Maybe we need a more pragmatic approach and swap over W and U and try the amp. There is a risk that the rewound transformer may still be unstable as there is some discrepancy in the ratio's compared to GJ's results of post #50 and changes in the winding capacitance may be a problem.

I would strongly recommend that the wiring to the anode/cathode of the output valves is checked while the transformer is out.

[sparkymike]

PJL
It is an original loom, so should be correct, but I will check anyway.
One thing I did spot one the tag board, next to one of the EF86 valve bases are penciled letters "U S". Maybe just a faulty valve in the past, or could be a faulty valve base with bad insulation. Will check. As a matter of interest, can the valve base be changed without removing the whole board ?
Mike.

[snowman_al]

Originally Posted by sparkymike

... One thing I did spot one the tag board, next to one of the EF86 valve bases are penciled letters "U S". Maybe just a faulty valve in the past, or could be a faulty valve base with bad insulation. Will check. As a matter of interest, can the valve base be changed without removing the whole board ?
Mike.

No it has to come out. BUT you can replace the socket pins in-situ if one is snapped. You get a 'spare' on pin 7 of both sockets. Have a very careful look down each hole and make sure both sides of the socket pins are there. If you are very careful you can re-form wide pins with a needle. (Switch off and discharge the caps before you try this!) Be careful if you use Russian versions of the EF86, they have 'pointy' pins and easily go down the side if the socket pin and deform them if not careful...

[PJL]

Originally Posted by sparkymike

PJL
It is an original loom, so should be correct, but I will check anyway.
One thing I did spot one the tag board, next to one of the EF86 valve bases are penciled letters "U S". Maybe just a faulty valve in the past, or could be a faulty valve base with bad insulation. Will check. As a matter of interest, can the valve base be changed without removing the whole board ?
Mike.

As you have no idea what the U.S referred to, I suggest you check the pins as Al has suggested and if they are OK, leave as is.

[sparkymike]

To PJL,
I did run a check on the anode connections as you said.
Wire X connects to the output valve next to mains transformer and
Wire Z connects to the output valve next to the tag board.
Wire Y connects to choke.
Mike.

[sparkymike]

At some time I would like to run a signal(music) into the amplifier without using my 22 preamp. Can I make a very simple test pre-amp to do this ?.
Transistor perhaps with just a volume control..
Mike.

[PJL]

Focus on getting the amp to work first. Where do U and W connect to?

The Quad II is not very sensitive but connecting a CD player direct might still be OK.